Condensation of Water, Styrene, and Butadiene Vapors Pure Components and Constant Boiling Mixtures F. B O N I L L A , T.CICHELL12
D A V I D A. E D W A R D S ' , C H A R L E S AND
MARIO
T H E J O H N S H O P K I N S U N I V E R S I T Y . BALTIMORE 18, M D .
Li
c
T h e condensation of water, styrene, and butadiene vapors, and of water-styrene and water-butadiene mixtures a t or near t h e i r constant boiling compositions has been studied in a 1-inch diameter a n d 8-inch long vertical condenser. W a l l thermocouples permitted t h e calculation of t h e f i l m coefficients of heat transfer; 300 runs were carried o u t . Pressure ranged f r o m 14 mm. absolute t o atmospheric for styrene, and 34 t o 100 pounds per square inch absolute for butadiene. T h e coefficients for water averaged 6% above t h e Nusselt theory and for butadiene
40% above. For styrene t h e y averaged 12970 higher t h a n theory. Assuming t h e vapor mixtures were a t t h e e q u i l i b rium composition a n d t h a t t h e condensate film consisted of t h e organic constituent alone, t h e Nusselt theory was found t o correlate t h e results w i t h t w o immiscible components m o r e consistently t h a n other available relations; deviations were i n t h e direction of obtaining conservative design. Coefficients for t h e system styrene-water averaged 43% higher a n d for butadiene-water 34% higher t h a n theory. Film Reynolds numbers ranged f r o m 9 t o 1460.
T
coefficients for the vertical tube could be suitably applied n-ith adequate accuracy to coefficients predicted for horizontal tubes. Simultaneously, a study of different metals for condenser tubes was initiated to determine vihich should be employed and IThich avoided on account of fouling by polymerization products. Details of this study are not reported here, but preliminary results indicated that polymer formed most rapidly on nickel and least on aluminum and stainless steel. Other metals tested were brass, copper, chromium-plated copper, Monel, and steel.
HE GR-S synthetic rubber industry requires the condensation of styrene and of butadiene vapors, as well as mixt'ures of styrene, butadiene, and ivater vapors. The plants involved had to be largely designed without benefit of pilot plant test's, and heat transfer data on these hydrocarbons and their aqueous mixtures were not available in the literature. The condensation of one-component vapors ordinarily follows the Xusselt relation (8) fairly well. HoLvever, dropwise condensation and other deviat,ions are at times obtained. I n t8he condensation of vapors of immiscible liquids one component preferentially wets the walls and condenses in a filnin-ise manner, the other condensing dropvise on the film of the former (9). Making- the usual assump'tion that in niixctures x i t h steam it is the organic compound that forms the continuous film, the Susselt equat,ion could also be employed to predict the coefficient of heat transfer in this case. Some experimental work in this field has been reported in t,he literature (1-3, 7 , 8) but there is no agreement on met,hods of correlat,ion of results. Thus, i t was decided to study the condensation of t8hese pure components and of their mixtures (6) vhile the GR-S plants were being construct,ed, to provide dat'a in case the plant condensers proved inadequate or increased capacity was desired. The plant condensers emplo)horizontal tubes. However, a vertical tube cooled on the outside was selected for t'his n-ork to provide better control of operating conditions. I t was felt that any observed departure from predicted 1 Present address, Glenn L. M a r t i n Company, Baltimore, hId. 2 Present address, Mellon Institute of Industrial Research, Pittsburgh, Pa.
Figure 1.
APPARATUS
The equipment employed for most of the runs is shown in Figure 1. The boiler was a No. 24 Thrush heater, employing steam inside the tubes to boil stvrene and/or water, and recirculating hot water to boil butadiene. An identical heater above the first one, also with steam or hot water inside the tubes, served as vapor mixer, entrainment separator, and foam breaker. In particular, it permitted more runs to be made with a single batch of styrene by breaking up the foam caused by polystyrene before it reached the test condenser. The vapors then rose through the test condenser, a 12-inch length of 0.0625-inch wall and 1-inch inside diameter copper tube jacketed for 8 inches a t the top by a length of 1.25-inch standard iron pipe with cooling water connections and thermocouple lead openings, as detailed in Figure 2. The two intermediate cooling n-ater thermocouples and the three mall thermocouples were made from 30-gage (Leeds & Northrup 1938 calibration) constantan wire with enamel and glyptal coverings inserted in a copper tube inch outside diameter. One purpose of the cooling water thermocouples was to faciliApparatus for Condensing H e a t tate the computing of the water side Transfer Coefficients
1105
INDUSTRIAL AND ENGINEERING CHEMISTRY
1106
film coet!icients of heat transfer. The cuuples were silver soldered and were calibrated at, room temperature, 100" C., and the melting point, of tin. T h e wall thermocouples were soldered into grooves l,'32 inch deep extending two thirds around the tube; escess solder was filed off to exposr the thermocouple tube and yield a smooth surface. Accurate thermometers gave the water inlet, and outlet temperatures. The inlet vapor thermocouple as a standard two-wire couplc in a well. The thermocouple,. were read with a portable preckion putentiomcter, and teiiiperatures v-ere probably accuratc: 1 0 0 . 5 - F. inr.ludinp errors in lopat#ion,
Vcl. 40, No E
nut ordinarily been c~mploycdaiid tht. >i;ixclLtrd fin ctficici~~,: formula ~i-ouldowrcorrwt. as t h r n-all temperature a t the ends would have started t o r e before either end \vas rmched. Furthermore, from the coi truction of the lvatcr inlet and uutlc: connections the woling ffertiveiii.;-i is probably lon.e~.:it one 0both ends; this is an error in the opposite direction. It is t h u s believed that no important error is introduced, a t least relativc to previous work, by ncglecting cnd effects in spite of t h e shortness of the test condenwr. This is also bornc out kiy the, , g m c agreement of the. Jvater runs with the Sussclt theory. The difference b e t m e n the temperature of the vapor, I , , a ~ i c that given by each tube wall thermocouple, to, is the lrjcal A; across the rondensatcx film and most nf the t,hirkness of the roppe: rube. Defining L- as the local over-all coefficient over the conden.:ii I~ tilm and tube wall and t~ as the condenser rvater teiiipera?llr(. thc appropria,tc different,ial equation:
dq = It'CdtL
=
rL(&- t " ) d A .
I
parated and integrated in Pithi'r of two ivays:
Kquatioii 2 is the standard inethod, and does not require tilt intermediate cooling w t e r temperatures for each value of I Equation 3, on the other hand, does not require the relation between the temperatures and position along the tube if t~ and t., artkiion-n a t thesame levels (assuming t , constant). As all of thrsc darn were obtained it was possible to check the data and tw( methods against each other. There was good agreement; but,k, equations gave roughly the same values of Ui. Although thtuse of Equation 2 Jvould have been somenhat simpler, Equation :i was act.ually used for all coefficients hereinafter reported. Theoretically, local values of (,-i at different positions down L ~ I iube may be obt,ained from the slope of the plot of t~ against 4 , iince Fquation 1 may be rewritten: Figure 2.
Detailed Drawing of Condenser
(t.c. indicates thermocouple junction)
'The uricondensed portion of the vapors then went tu ail ausiliary or vent condenser consisting of a 20-inch copper tubc of 1 iiich inside diameter jacketed over most of its length. The condensate returned to the bottom of t'he boiler. Above t'he auxiliary condenser a line went to an inverted gas cylinder to minimize p sure fluctuations, and to a water aspirator for vacuum r u m ( nitrogen cylinder for runs above atmospheric pressure. Cooling wat,er for the test condenser came from a eonbraill head tank, arid the rate of f l o ~ Ivas obtained by direct n-eigiiing. 'The test condenser and the ,n-ater lines were well lagged up to yeveral inches beyond each thermometer well. A connection tn Bush the apparatus with live steani \vas provided to decomposc Iziiy explosive compounds t'hat might possibly form. To make a run the boiler was tn-o thirds filled with tht: desired compound or mixture, the pressure was set, and then the cooling water and heating fluid were turned on. K h e n a stead\- state was reached, all possible temperatures and pressures mr'e r e a d The test condenser cooling water rate was adjusted to yield a temperature rise of the order of niagnit'ude of 10" to 20" F., to obtain reasonable accuracy yet not a large variat'ion in will temperature. All tests were run with an appreciable temperature rise of the auxiliary condenser cooling water, to avoid air in the test condenser. Runs were continued on a given charge until readings became erratic, or failed to check earlier ruiis under identical conditions, The apparatus was then cleaned and a fresh charge inserted. COMPUTATIONS EMPLOYED
'The rate of heat transfer through the test condenser 6 % take11 ~ t ~ sequal to the rate of heat gain of the cooling water. S o correction was applied for heat transferred through the thermal insulation because the water was norrnallv near room temDerature and the estimated error in practically every run was well under 1 yoof the heat gained by the test condenser cooling water. T h e heat transfer area was taken as 0.1745 square foot, the inside area between the t x o outer rubber stoppers. xo corlcction for added area a t the ends was applied. Tn prcvions M orli I t ha-
Acrually, insufficient points for each run were available for t h i > purpose, and an integrated Equat'ion, 2 or 3 is necessary. On equating Equations 2 and 3 it is seen that the two value3 U: L't,m will be equal only if ( f , - t o ) is constant. It was due to the small magnitudc of the variation of ( t , - L) in these tests thai rhe two equations gave similar results. Equation 3 gives thriiiean value of Ui when the local value of Vi is integrated 10vt.-
IT,dd,. I t is evidently the prop"
tliu area---namely,
valuti of C'L,,o to employ when It has been averaged by plot?iilL
'-
If
against q, as is frequent in design procedures.
Equation 2 gives the mean Ui by
L'*
V i which s2ioul(i f
P
he used only in design work in conjunction with the mean value 01 ~t integratcd over t,he area. This mean I t is much more difficulr to predict ahead of time and thus Equation 3 gives the more us('ful value of This disrussion of course would hold equalli for an over-all coefficient or for a film coefficient of heat transfer. Subsequently the values of hi,m were corrected for nonuniforri, by dividing them by the factor Ft, quoted in (9). This factor evidently yields the value of hi which would have been obtaineb a t the uniform value of Iti necessary to yield the total rate o! condensation actually observed. It, dccreascd the corficicnts *r,., rioii for
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0
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1
74700
273
1 1
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1
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60.500
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53
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1610 1100 I010 1133 1188
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an 245 .,-,J -
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263 209
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772 600 400
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212
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213.2 214.; 212.,
212.0 212 b
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21°C
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123. 123
1'31.8 I 3: , ,
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288 30s
309
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311 312 313 318 311r
239 239 242 2337 234
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98
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8.99 25 3
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30.4 37,33 31.8
lI covered, and probably has no theoretical value, nor should it be extrapolated. The principal reason for drawing it is that if the water droplets shed so easily on vertical pipes as not t o affect the heat transfer n hen the mixture is being condensed, they ma! also not affect the ripples or other cause of high coefficients obtained Kith pure styrene. Thus it is possible that the entire line as drawn may hold for styrene Kith or xithout water present, a: well as for each case over the corresponding limited range tested. i f only the points on Figure 4 for styrene-mater mixtures arc i*onsidered,least squares gives the following line:
ti-ith rhe vapor mixtures, t, was taken as the trniperature 81 rhich the sum of the yapor pressures of n-ater arid the hydxo:arbon equaled the observed total pressure. The olxwved vapor r>eniperaturea t the t w t condenser inlet in many runs was close :o the calculated temperature, which is some confirmation thai -he vapor composition equaled the calculated value. I n other where the indicated uncertainties are for the 95% confidenor ':uns, the observed vapor temperature was several degrees lone1 level. 31 several degrees higher than calculated. I n some runs it \vas a': The butadiene-n-ater runs (Figure .5) fall among the butadiene ilnuch as 35' t o 40' F. higher. especially a t l o n pressures (Tablc runs, as might have been expected from the small proportion of water present (from 1 to 2 mole %). The eight runs carried out U, I n plotting Figure 4, hoiwver, it vias observed that thiyield an average constant of 1.985 in Equation 6 (average deviaieviation b e b e e n calculated sat,uration and observed vapoi tion 0.09), 3 i c r above the Susselt theory 8-eniperaturcs eausrd riel trend in the points. Therefore, it T\-R,iszumed always that the rapor composition v a s a t or fairly closi Eight additional r u m n e i e carried out (111 nitter dud btj ie11r ro the equilibrium value, and tlie observed temperatures n-err to nhich a tiarc uader Ic;i of butadiene, insufficient to affect lisregarded, Possibly the low observed temperatures w r e dur the phvaical piopPrtip. of the stvrentx appicciably, had bcen ro the thermucouple n-all conling in contact Ivith euhcooled coiladded. These pointq fell among the nater-stvrene points of lensate, and the liiqli one; due tt? huperhenting o n the boiliriy Figure 4. Similaily, ten additional runs on water and butadiene surface or in the upprr hrater. If the vapor is superheated tht, nith under lC; stIrene added agreed ne11 111th the ~ a t e r - b u t a ~ direction from the constant :oniposi-iun ma> ~ l r v i ~ini i citheidiene points. boiling mixture, but an incrt,ase in hydrocarbon contcnt iq rii(11I Rune for nater in the diffrient prmsure ranges (Figure 3 :ikcly because of better wetting of the boiling mrface. This would mean that the points affected should actually be plotted somen-hat to ihe right of their location in Figure 4, as Reynolds numbers would be increased. It. does not seem iikely that any such correction would do mort Fhan increase the agreement of the loKer pressure soints n-ith McAdand curve B-B, which is in the iirection of conservative design. It would have been desirable t u include equip.iient for sampling and anal>-zingthe condensate from t,he test condenser. However, this was not ione in order to simplify the apparatus and pro7edure and to decrease the liquid holdup. From the pressure or mole ratio, the might ratio of wat,er t o hydrocarbon was calculated and, Figure 4. Condensation of Styrene and I t s Saturated Mixture w i t h bn-ith the latent heats of condensation a t the Water a t Various Pressures given temperature, r was computed for t,he hyAll styrene points are to the right of the center and all mixture points to the left. drocarbon portion only of the condensate. UsApproximate absolute pressures: 4 = 15 to 75 mm.; A = styrene, 88 t o 115 mm. and mixture, 98 to 202 mm.; x = styrene, 195 t o 248 mm. and mixture, 239 to 243 mm.; ing the physical properties of t,he hydrocarbon = 760 mm. A = Nusselttheory; B = M c A d a m s recommended equation: C = average done t.he Kirkbride plot wa? then prepared. line through above points
INDUSTRIAL AND ENGINEERING CHEMISTRY
1112
Table I I I .
Constituents Styrene
+ water
Uutadieiie
+ water
Pressure Range, Absolute
Comparison of Correlations for Condensation
Tlieorerical
760 mni. 240 tnin. 100 inin. 20 to 40 I,.’.!. 40 t o 60 p . , . ~ . GO t o 80 li i. 60 min. to 100 p.s.i.
Vol. 40, No. 6
a4g{We served
40.8 3!L3 39.3
(lii,w)
(e)
Haaelton and Baker Predicted (hi,m)
470 456
444
433
412
477
0.946 0.95 o.sfi3
Baker and Tsao Predicted (hi,m)
750 720
720
Susselt
Tiieorya
(22)
::%?I
1.43
11c.idaiuu Eciuation
( hi,,:
